A spot, freckle, and pigmentation after skin is exposed to the sun refer to a condition in which melanogenesis is sharply accelerated by activation of pigment cells (melanocyte) which exists in the skin. There has been known a skin external preparation (especially skin-whitening agent) to prevent or ameliorate such skin pigment troubles containing ascorbic acids, hydrogen peroxide, colloidal sulfur, glutathione, hydroquinone, or catechol. However, it is also known that such whitening agents sometimes effectively exert their actions but sometimes do not exert the actions the reason for which may be attributed to poor skin penetration of the applied products.
Conventionally, the skin whitening is tried by mixing material having inhibition function against tyrosinase such as hydroquinone, ascorbic acid, kojic acid, or glutathione with cosmetic such as essence or ointment for external use. However, although hydroquinone shows a prescribed effect of whitening, the mixture amount of the same should be restricted to minimum since the same may seriously irritate the skin or may cause allergic problems. In case of ascorbic acid, since the same is easy to be oxidized, cosmetic mixed with the same has problems of discoloration and change of scent, and in case of kojic acid, the same is restricted to be used since the same is unstable. Further, thiol compound such as glutathione or cysteine has a peculiar bad smell and low absorptiveness to skin.
U.S. Pat. No. 6,514,538 discloses a skin whitening method comprising applying a whitening endermic liniment onto skin, said whitening endermic liniment comprising an extract from a plant of the Solanaceae family (Solanaceae), genus Withania (Withania), wherein application of said liniment upon skin causes suppression of tyrosinase activity and melanin production therein.
U.S. Pat. No. 5,824,327 discloses a skin whitening cosmetic composition and in particular to such a composition which is anhydrous and incorporates kojic dipalmitate.
U.S. Pat. No. 4,847,074 discloses a kojic acid containing whitener cosmetic composition that includes cyclodextrins for improved stability, i.e. to compensate for color changes.
PCT publication No. WO 2002/055047 discloses a skin whitening compositions comprising arbutin and glucosidase.
U.S. Pat. No. 5,629,021 relates to micellar nanoparticles and methods of their production.
EP Patent No. EP 506197 B1 discloses an aqueous suspension of solid lipid nanoparticles for topical use.
EP Patent No. EP 671903 B1 discloses topical compositions in the form of submicron oil spheres.
Most of the topical preparations contain vehicles comprising permeation enhancers, solvents, and high amount of surfactants to achieve these goals. But use of these agents is harmful, especially in chronic application, as many of them are irritants.
Therefore, despite of the wide availability of products for skin whitening, there exists a need to develop topical preparations which does not involve use of such agents as described above to facilitate drug permeation through the skin, improved onsite delivery and reduced skin irritation.
The compositions of the invention overcome all the commonly encountered problems as exemplified above.